This invention relates generally to interior trim panels for automobiles and more particularly to automotive interior trim panels that have a flexible plastic covering attached to a structural substrate.
U.S. Pat. No. 4,900,989 granted to Takashi Nagase and Yoshio Taguchi Feb. 13, 1990 discloses an automotive trim panel that comprises an expanded polyvinyl chloride skin that is made by a double slush molding process to produce a thin skin of about 0.1 mm to 0.5 mm thickness with a thin foam backing of about 0.4 to 3.0 mm thickness. The expanded polyvinyl chloride skin or covering is then placed in a foaming mold and integrated with a steel core plate by foaming an intermediate flexible polyurethane layer in place.
According to the patent, the use of an expanded polyvinyl chloride skin eliminates or substantially reduces the migration of plasticizer in the polyvinyl chloride to the polyurethane layer and thus avoids degradation, cracking and discoloration of the polyvinyl chloride skin.
This proposal, however, does not solve the underlying problem inherent in the use of a polyvinyl chloride skin which is not environmentally friendly because of the need for a plasticizer to achieve low temperature flexibility. Another environmental concern, particularly in Europe, is the possible escape of chlorine and consequent damage to the ozone layer. Another drawback of the proposal is that the polyvinyl chloride foam does not adhere well to the intermediate polyurethane layer and consequently it is often necessary to apply a urethane coating to the polyvinyl chloride foam backing before the polyurethane layer is foamed in the foaming mold.
Another known method that is similar to the above method foams a rigid polyurethane foam in place after the expanded polyvinyl chloride skin is placed in the foaming mold. This eliminates the need for a steel core plate. However this known method has the same problems and drawbacks discussed above in connection with the expanded polyvinyl chloride skin.
U.S. Pat. No. 4,769,278 granted to Tomobisa Kamaimura, Noriyoshi Suzuki, and Takashi Imaizumi Sep. 6, 1988 also discloses methods of manufacturing interior trim panels using a double slush molding process. For instance in the "prior art" method of FIG. 5 the expanded vinyl skin is still slush molded. However, a preformed rigid core is set against the vinyl foam backing layer while it is still soft to join onto the expanded vinyl skin. According to the patent this method has several problems including difficulty in forming the vinyl skin layer evenly, difficulty in controlling the thickness of the vinyl foam layer and the formation of pockets of air between the vinyl foam layer and the rigid urethane core.
The patent then considers and rejects the concept of forming a rigid urethane core by pouring hard urethane resin onto the vinyl foam layer for several reasons.
The patent then proposes as a solution, the bonding of a preformed laminated substrate comprising a rigid core having a resilient urethane foam or felt covering to the vinyl foam layer of the expanded vinyl skin after the vinyl foam layer cures. This patented solution, however, has the same problems and drawbacks discussed in connection with the earlier patent. Moreover, the method is more complicated and more expensive.
U.S. Pat. No. 5,073,318 granted to Milo L. Rohrlach and William J. Hall Dec. 17, 1991 discloses a door inner panel of a motor vehicle comprising a substrate of rigid polyurethane foam reinforced with glass fibers, an elastomeric facing layer of flexible polyurethane, and an intermediate layer of soft resilient polyurethane foam between the facing layer and the substrate which extends sufficiently over the area of the panel to adhere the facing layer to the substrate. The patent specification does not mention any particular advantages for the preferred polyurethane materials and suggests using other alternative materials. For instance, reinforced polyesters, wood dust filled polypropylene or phenolic bonded fabric fibers are indicated as suitable for the substrate while flexible acrylic, polyvinylchloride and other polymeric materials are mentioned for the facing layer.
The door inner panel is made in stages in which the rigid reinforced substrate is molded in a first die set. The molded substrate is then positioned in an upper die part of a second die set. The lower die part of the second die set is sprayed with a paint and then a second layer of polyurethane elastomer is applied curing to a dense soft polyurethane facing layer. After the facing layer has at least partly cured, foam forming material is placed over the facing layer and the die parts of the second die set are closed. The foam forming material then cross links into a soft resilient polyurethane foam that adheres to the facing layer and the substrate over most of the area of the panel.
The Rohrlach method like that of the Kamaimira patent discussed above is also complicated and expensive.